Two main types of bulk freight tank containers are known. One of these is commonly called a frame tank and comprises the cylindrical tank itself, two rectangular end frames, and girders joining the end frames. The tank is supported by the end frames and girders and little problem is experienced in constructing the frame tank with sufficient strength to prevent the cylindrical tank itself from being damaged as a result of twisting, sagging or flexing. However, a frame tank does have the disadvantage that it has a comparatively great mass and its carrying capacity is reduced commensurately. GB No. 1362461 discloses a tank of this type.
The second type of bulk freight tank container is known as a beam tank. This consists of a cylindrical tank and two end frames. The tank constitutes the only structural element joining the end frames, and is thus unsupported except at its ends. Consequently, it is capable of twisting and sagging. Great care must be taken in constructing the so-called saddles which join the tank to the end frames. If the saddles are not properly constructed then twisting and flexing of the tank can occur to such an extent that it results in damage to the tank and/or to the saddles, or in the saddles separating from the tank or end frames. GB No. 2168415 A, GB No. 1520213, and GB No. 2083445A all disclose beam tanks.